I feel your pain. I used to squat/deadlift competively and now can't due to disc issues in my lower back. One leg exersize I've found that I can go fairly heavy on and not stress my lower back too much is dumbbell step-ups. I hold a dumbbell in each hand and then step up onto a bench or box. I started with like 40's and now can grab a set of 100's and do 8-10 each side. You don't have to bend at the waist like a squat so it doesn't hurt but still feels like I'm getting some "heavy" work on my legs. Wear a belt, watch your form, and be careful not to hyper-extend your knee stepping back down. Good luck and keep training!

Thanks jj45, I will definitely incorporate that into my leg day.